Olefin based polymers (polyolefins) are widely used in various applications due to their being chemically inert, having low density, and low cost. Applications include those related to adhesives, tie layers, skin layers, films, fibers, articles, laminates, overmolded parts, co-injected parts, and combinations thereof.
Polyolefin adhesives may be formed into various films, which may be laminated to, coated on, or co-extruded with various substrates. The film and the substrate may be combined with other materials to form a structure having a plurality of layers, each layer having a specific purpose. Packaging laminates, for example, may comprise a plurality of layers, such as a configurationally rigid core layer of paper or paperboard, an outer liquid-tight layer, an oxygen gas barrier such as a mid-layer of aluminum foil, and/or other layers depending on application needs.
To provide effective adhesion, it may be preferable that good bonding strength or intimate integrity between the layers be achieved for most applications.
However, relatively non-polar olefin based polymers do not normally adhere well to substrates which are more polar than they.
Particular applications may require a “soft” elastomer-like adhesive, which may be obtained using an apolar fluid and/or a non-functionalized plasticizer (NFP) in combination with an adhesive. However, bond strength of the apolar fluid and/or NFP modified polyolefin composition to polar substrates, such as polyester, corona-discharge-treated polyolefin, ionomer, nylon, poly(vinyl alcohol), poly(vinylidene chloride), polycarbonate, metals, glass, and the like is generally low due to lack of surface activity and/or fluid/NFP enrichment at the adhesive-surface interface. In addition, there is a need to improve the melt processability of adhesives known in the art.
Thus, there remains a need for an adhesive, preferably a pliable adhesive that will intimately bond to both polar and non-polar substrates. This need extends to an adhesive that exhibits a superior durability of bond strength under various temperature conditions and in the presence of aggressive products.
In addition, there is a need for an adhesive composition that may function as a tie layer. Such an adhesive composition may need to demonstrate adhesion between a variety of polar and non-polar substrates.
Numerous references are directed to compositions comprising syndiotactic polypropylene as an adhesion promoter. Examples include Japanese Patent Application 01-152448, Japanese Patent no. JP2824082, U.S. Pat. Nos. 5,476,914, 6,184,326, and 6,245,870 all assigned to Fina Technology Inc. which are directed to vanadium catalysts capable of producing compositions comprising syndiotactic polypropylene having greater than 80% r dyads. However, they do not disclose a functionalized propylene copolymer adhesive composition.
U.S. patent application Ser. No. 10/962,312 filed Oct. 8, 2004 discloses thermoplastic compositions of polypropylene for use in molded articles. The reference discloses maleated polypropylene copolymers having 0.25 wt % maleic anhydride, but is silent with regard to adhesion or adhesive properties.
Further, U.S. Pat. No. 6,656,385 to Wang et al. (Wang) is directed to a hot melt adhesive comprising about 15 to about 70% syndiotactic polypropylene and amorphous poly(alpha-olefin) along with a tackifier, optionally a plasticizer and/or a stabilizer. Wang defines syndiotactic polypropylene to have greater than 70% r dyads. As such, Wang does not disclose a functionalized propylene copolymer adhesive composition.
U.S. Pat. No. 4,822,688 to Nogues is directed to an adhesive composition comprising polypropylene modified by grafting with an acid anhydride which is further reacted with a compound bearing at least two groups such as a polyol or a polyamine. While Nogues discloses functionalized polyolefins, the reference does not disclose functionalized propylene copolymer adhesive promoters that improve adhesion.
WO 02/036651 discloses various maleated propylene based polymers and states at page 26 that such polymers may be useful as adhesion promoters between a polypropylene matrix and glass fibers or compatibilizers in polyamide/polypropylene blends or to increase the elongation at break of glass filled polyamide/polypropylene blends.
U.S. Pat. No. 6,310,134 (and related divisional US 2002/0010257) discloses a solvent based primer that is apparently a combination of lower molecular weight modified polyolefin with a selected solvent. The disclosure also does not specify the triad tacticity.
EP 1 366 087 discloses a non-chlorinated adhesion promoter in which a modified polymer is used with selected solvent as a primer. Example 2 uses an unmodified polymer comprising 80 mol % propylene derived units with a heat of fusion of approximately 5.2 calories per gram but there is no indication of the triad tacticity level.
U.S. Pat. No. 6,627,723 discloses adhesives comprising propylene based polymers where the polymer has, among other things, a heat of fusion of from about 30 to about 80 J/g.
U.S. Pat. No. 6,747,114 discloses adhesives comprising propylene based polymers where the polymer has, among other things, a specific storage modulus (G′) in combination with a specific diad distribution of less than 1.07.
US 2006/0020067 discloses blends of functionalized syndiotactic rich polyolefins.
Accordingly, there remains a need for a polymer compositions comprising a functionalized propylene copolymer which demonstrates a benefit in adhesive properties to both polar and non-polar substrates, while preferably having softness and or flexability.
Additional references of interest include: U.S. Pat. Nos. 6,207,606, 6,258,903, 6,271,323, 6,340,703, 6,297,301, 6,184,327, 6,225,432, 6,342,574, 6,147,180, 6,114,457, 6,143,846, 5,998,547, 5,696,045, 5,350,817, and 6,659,965, US 2001/0007896 A1, WO 00/37514, WO 01/81493, WO 98/49229, WO 98/32784, WO 2004/014998, WO 2003/040095, WO 2003/040201, WO 2003/040202, WO 2003/040233, WO 2003/040442, and WO 01/09200.
Accordingly, there remains a need for polymer compositions comprising a functionalized propylene copolymer and a plasticizer which demonstrates a benefit in adhesive properties to both polar and non-polar substrates.